Subcutaneous tetrahydrobiopterin was administered to 5 patients with dementia of the Alzheimer type. No gross change in neurologic examination or significant adverse effects were observed. Cerebrospinal fluid (CSF) drug and monoamine metabolite concentrations were evaluated. Intravenous haloperidol was administered to two healthy subjects to test the dopamine system in aging. No significant adverse effects were seen. CSF monoamine metabolites, plasma haloperidol and prolactin concentrations and quantitative cognitive and motor tests are being evaluated.